This invention relates to a brakeable hand truck, particularly one having a hydraulically-operated disc brake system.
In the commercial transportation of goods where many large and heavy packages must be loaded and unloaded manually, the use of a hand truck suitable for handling such heavy loads is very helpful. One requirement of such a hand truck which has become increasingly important for safety reasons is that it have an adequate braking system, that is, a braking system which will enable the operator to restrain a heavily loaded hand truck as it is moved down an inclined ramp and properly guide and balance the load without having to exert too much physical effort. Without adequate and reliable braking, a heavily loaded hand truck can pull the operator forcibly down an incline, causing him to lose balance and injure both himself and the load.
In addition, it is particularly desirable that a brakeable hand truck be of light-weight construction so that it may be lifted and carried maually with little effort, and that it utilize pneumatic tires in order to increase its stability against tipping by reducing the shocks from moving over bumps or objects.
One solution to the braking problem heretofore applied is a bar-type brake comprising a metal bar which rubs against the rubber surface of the hand truck tires when actuated, as shown in Honeyman U.S. Pat. No. 3,276,550. One drawback of the bar-type brake is that when the tires get wet, as frequently is the case, the friction between the bar and the tire surface is greatly reduced and the brake becomes considerably less effective. Also both the bar and the tire, which comprise the friction producing parts, tend to wear rapidly which makes the use of pneumatic tires impractical since they would have to be frequently replaced, and necessitates considerable expense in the frequent replacement of the metal bar. Finally, tires with a significant amount of tread cannot readily be used with a bar-type brake to enhance the tires' grip on the ground because the spaces in the tread would considerably reduce the brake's friction-producing surface area and tend to cause grabbing as the bar catches the edges of the tread.
Another approach to the braking of hand trucks is to use a strap-type brake wherein a strap of flexible material is wrapped around a drum mounted to rotate in unison with a wheel so that the strap may be pulled tightly against the drum to produce braking friction, as shown in Barron U.S. Pat. No. 3,422,930. A principal problem with the strap-type brake is that dust and dirt tend to collect between the strap and the drum which diminishes the friction-producing surface area, thereby reducing the effectiveness of the brake, and frequently causes uncontrolled grabbing of the brake. When a heavy load is being moved down an incline such grabbing can be very dangerous since, upon abrupt stopping of the truck, the momentum of the load may cause it to be thrown off the hand truck and possibly cause the hand truck to pivot forwardly over its axle, thereby violently pulling the operator forward and injuring him.
A further apparatus for braking a hand truck utilizes a shoe-type braking member which moves outwardly against the interior surface of the hand truck wheels, or a brake drum mounted to rotate in unison with the wheels, as shown in Smith U.S. Pat. No. 2,246,147. Like the strap-type brake such a system utilizes a horizontally-oriented friction surface which tends to collect dust and dirt, as well as water, thereby leading to degradation of its braking ability or possible uncontrolled grabbing.
Thus there is at present a need for a brakeable hand truck which provides ample braking force which may be reliably applied in a smooth, modulating fashion with little effort, avoids wear of the tire rubber, is sturdy and long-wearing while not adding appreciable weight to the truck, and is unaffected by moisture and dirt.